Many times printed documents are needed to prove ownership of some valuable resource. Real estate deeds and stock certificates are examples of these types of documents. Since these documents represent valuable resources and can be used as collateral for a loan, making forgery difficult and the ability to identify the rightful owner is important.
One threat to the use of these documents is that someone will produce a fake document that looks like the original. Another threat is that a legitimate creator of such documents creates unauthorized documents that don't represent real value. Yet another threat is that a legitimate document will be stolen or copied.
Rightful ownership is often proven with a “wet signature”, which is an original signature written on a piece of paper, as opposed to a fax copy or to an agreement offered verbally or electronically. However, documents requiring a wet signature are vulnerable until the documents are signed. Also, a signature may be forged. Furthermore, illiterates and some handicapped people may not be able to write a signature.